An engine is provided with an ignition coil having a coil main body constructed by, for example, coaxially providing a primary coil with a secondary coil. The primary coil is constructed by winding a wire around a primary spool to form a primary winding, and the secondary coil is constructed by winding a wire around a secondary spool to form a secondary winding. A center core, which is formed of a magnetic material, is provided on the radially inner side of the primary and secondary coils. An outer core, which is formed of a magnetic material, is provided on the radially outer side of the primary and secondary coils. Thus, the center core and the outer core construct a magnetic circuit.
The secondary coil has a high voltage end defining a plug mount portion to which a sparkplug is provided. The plug mount portion has a cap mount portion, which is in a cylindrical shape, and extends from a spool constructing the primary coil or the like. The cap mount portion is attached with a plug cap formed of rubber. The plug cap has a fitting hole accommodating a coil spring electrically conducted with a high voltage winding end of the secondary coil via a high voltage terminal. The sparkplug is mounted to The plug mount portion by fitting an insulator portion of the sparkplug into the fitting hole. The sparkplug has a terminal portion in contact with the coil spring.
For example, an ignition coil is disclosed in U.S. Pat. No. 6,836,203 B2 (JP-A-2003-163126). In this structure, an intermediate portion of the coil spring is not steadily supported, and the intermediate portion may be radially deformed.
When the intermediate portion is largely deformed, electric contact between the coil spring and the sparkplug may not be maintained. In addition, when the intermediate portion is largely deformed, high voltage electricity passing through the coil spring may leak to low voltage components.
According to JP-A-8-100753, an ignition coil includes an ignition coil portion (coil body) and a socket. The ignition coil portion (coil body) includes a primary coil and a secondary coil, and is located outside a plughole of an engine. The socket accommodates a spring electrically conducted with a high voltage winding end of the secondary coil. The socket is inserted into the plughole of the engine. In this structure, the socket supports the spring.
However, in this structure disclosed in JP-A-8-100753, the coil main body is outside the plughole, and this structure cannot be directly applied to a stick type structure in which the coil main body is inserted into the plughole.